Finally, we briefly discuss the problem of constrained deformation where the sheet is unilaterally constrained to adhere to an externally imposed rigid shape. An example is afforded by the problem of squeezing a sheet of paper inside a hollow sphere (or inside our fist). The sheet responds by crumpling and developing a distribution of kinks and creases [1]}. A simpler example is to try to fit a sheet of paper inside a hollow cone [2]}. This yields a developable cone (conical singularity with \(s=0\) ) such that there are portions of the of the sheet directly in contact with the outer rigid cone and portions which are folded away. A conical deformation in such a scenario would satisfy the equilibrium of the form \(D\Delta ^2 W - [\Phi ,W]=B\)  where \(B\)  is the distributional contact force supported over the region where the sheet is in contact with the rigid cone. If the constrained deformation has been achieved by applying a point force then the singular force should be incorporated within \(B\) .
